The proposed studies focus on the development and characterization of new highly targeted gene therapy approaches for the systemic treatment of aggressive B-cell lymphomas with an emphasis on mantle cell lymphoma (MCL). Lymphomas are subdivided into Hodgkin's lymphoma (HL) and non-Hodgkin's lymphoma (NHL), of which in the United States more than 85% are NHL. MCL is an aggressive form of B-cell NHL with a very poor prognosis. MCL comprises 5-10% of NHL cases, has a median survival of about 4 years, and a long- term survival rate of less than 15%, which has not significantly changed in the past 20 years. Currently, there is no accepted standard of care for the treatment of MCL and the disease is considered incurable. Therefore, novel therapeutic approaches are urgently needed. In the strategies described in this application, MCL targeting will occur via two mechanisms: 1) through the targeting of a tumor-associated antigen (TAA) on the surface of malignant B cells and 2) through the selective expression of toxic genes using a cell-specific promoter. TAA on the surface of cancer cells serve as excellent targets for immunotherapy. Therefore, the first level of my targeted strategy will occur through the use of a mouse/human chimeric antibody-avidin fusion protein specific for the transferrin receptor (TfR). This receptor is an attractive target for cancer therapy due to its elevated expression on the surface of cancer cells, its ability to internalize, and its central role in the cellular pathology of cancer. However, the TfR is expressed on some normal cells at various levels. In order to further improve malignant cell targeting, the second level of my targeted strategy focuses on limiting the expression of toxic genes to malignant cells by using the immunoglobulin promoter. The central hypothesis of the present proposal is that TfR overexpression on the surface of MCL can be used as an effective target for TfR- mediated gene delivery, for which the transgene will be transcriptionally restricted. Since tumor targeting will occur on two levels, I also hypothesize that this strategy will be extremely effective in eliminating malignant B cells in vivo without the severe side effects that limit the efficacy of most cancer therapeutics. The antibody-avidin fusion protein that targets the TfR is a unique drug since it serves as a universal delivery system for a wide variety of biotinylated agents. The antibody-avidin fusion protein will be conjugated to either biotinylated DNA or biotinylated lentiviral vectors in order to deliver a toxic gene into malignant B cells by receptor-mediated endocytosis. The use of two independent and non-exclusive gene therapy strategies is proposed in this application. The first gene encodes the toxin saporin, a ribosomal inactivating protein that is derived from the plant Saponaria officinialis. Saporin is a single chain toxin that cannot enter cells by itself due to the lack of a cell-binding domain. Saporin is a highly toxic and once inside the cell it inhibits protein synthesis through its N-glycosidase activity that leads to the inactivation of the 28S ribosomal subunit. The second gene that will be used encodes a chimeric yeast enzyme (FCU1) that consists of cytosine deaminse (CD) and uracil phosphoribosyltransferase (UPRT). This enzyme converts the prodrug 5-fluorocytosine to the toxic metabolites 5-fluorouracil (5-FU) and 5-fluorouridine 5'monophosphate (5-FUMP) and thus is an antibody- directed enzyme prodrug therapy (ADEPT) approach. The prodrug will be converted to its toxic metabolites within the tumor microenvironment. It is expected there will be a bystander effect associated with ADEPT therapy since the toxic metabolites can be released from targeted cells and taken up by non-targeted malignant cells in the tumor environment as well as stromal cells that support the growth of the malignant cells. Importantly, these two strategies can be used in the future in combination to maximize their anti-tumor effects. The use of this dual targeting strategy using either toxic gene is expected to increase the anti-tumor activity compared to singularly targeted agents, as well as eliminate the potential systemic toxicity of the treatment. To execute this project I propose three specific aims: Aim 1: Reporter gene vector construction and in vitro optimization of gene delivery. Aim 2: Toxic gene vector construction and in vitro evaluation of targeted anti-cancer activity. Aim 3: Evaluation of toxicity, pharmacokinetics, and anti-tumor activity in animal models. This project is expected to result in important advances not only in the fields of cancer gene therapy and treatment of MCL, but also in my career development. In fact, many new skills will be acquired that will increase my knowledge and research experience. This training will aid in the future preparation of grant proposals that will allow me to become a better candidate for an academic faculty position at a leading institution, which is my long-term goal. It is my goal to become an independent investigator to better understand cancer cell biology in order to develop new therapeutics that will help reduce the pain and suffering encountered by cancer patients. The outstanding research environment at UCLA, the guidance from my experienced mentors, and this award will greatly facilitate my success in reaching my goals and will open a new dimension in my professional development.